Orthogonal Frequency-Division Multiplexing (OFDM), also referred to as “multicarrier modulation” (MCM) or “discrete multi-tone modulation” (DMTM), splits up and encodes high-speed incoming serial data, modulating it over a plurality of different carrier frequencies (called “subcarriers”) within a communication channel to transmit the data from one user to another. The serial information is broken up into a plurality of sub-signals that are transmitted simultaneously over the subcarriers in parallel.
By spacing the subcarrier frequencies at intervals of the frequency of the symbols to transmit, the peak power of each modulated subcarrier lines up exactly with zero power components of the other modulated subcarriers, thereby providing orthogonality (independence and separability) of the individual subcarriers. This allows a good spectral efficiency (close to optimal) and minimal inter-channel interference (ICI), i.e. interferences between the subcarriers.
For all these reasons, OFDM is used in many applications. Many digital transmission systems have adopted OFDM as the modulation technique such as digital broadcasting terrestrial TV (DVB-T), digital audio broadcasting (DAB), terrestrial integrated services digital broadcasting (ISDB-T), digital subscriber line (xDSL), WLAN systems, e.g. based on the IEEE 802.11a/g standards, cable TV systems, etc.
However, the advantage of the OFDM can be useful only when the orthogonality is maintained. In case the orthogonality is not sufficiently warranted by any means, the performances of the OFDM system may be degraded due to inter-symbol interference (ISI) and inter-carrier interference (ICI).
This could happen as a result of synchronization issues between the clocks of the emitter and of the receiver of the OFDM system. These issues comprise:                Symbol Timing Offset (STO) and,        Carrier Frequency Offset (CFO).        
Carrier Frequency Offset is notably caused by the mismatch of the oscillators of the emitter and of the receiver of the OFDM system, the nonlinear characteristic of the wireless channel and the Doppler shift when the emitter and/or the receiver are moving.
Even small frequency offsets can dramatically harm the signal to noise ratio (SNR) and the bit-error rate (BER). In particular, OFDM systems employing time-domain differential demodulation are very sensitive to CFO.
Therefore, accurate CFO estimation and correction algorithms should be implemented so as to avoid performance degradation.
Another issue that can arise is called Symbol Timing Offset (STO) corresponding to a lack of synchronization between the received symbols and the receiver's circuitry.
FFT (Fast Fourier Transform) and IFFT (Inverse Fast Fourier Transform) are the fundamental functions required for the modulation and demodulation at the transmitter and receiver of the OFDM systems. In order to take the N-point FFT in the receiver, it is required to get the exact samples of the transmitted signal for the OFDM symbol duration. A typical way to achieve this consists in performing a symbol-timing synchronization to detect the starting points of the OFDM symbols (with the cyclic prefixes removed).
This synchronization consists in an estimation of the STO (Symbol Timing Synchronization), and in a compensation based on this estimated STO.
The invention proposes a new method to estimate the STO, presenting a better accuracy that the methods according to the state of the art.